Shrunken bag made from biaxially stretched, VLDPE film

ABSTRACT

Heat-shrinkable films suitable for packaging food articles such as frozen poultry, primal meat cuts, and processed meat products. In one embodiment, the film may be a biaxially stretched monolayer film of a very low density polyethylene copolymer. In another embodiment, the film may be a biaxially stretched multilayer film comprising a first outer layer of an ethylene-vinyl acetate copolymer, a core layer of a barrier film such as a polyvinylidene chloride copolymer or an ethylene-vinyl alcohol copolymer, and a second outer layer comprising a blend of an ethylene-vinyl acetate copolymer and a very low density polyethylene copolymer. The multilayer film is preferably made by coextrusion of the layers. The films are fabricated into bags useful for the aforementioned purposes. The bags have improved toughness.

This application is a Division of prior U.S. application Ser. No.07/779,676, filed Oct. 21, 1991, now U.S. Pat. No. 5,256,428, which is aDivision of application Ser. No. 07/501,986, filed Mar. 28, 1990, nowU.S. Pat. No. 5,059,481, which is a Continuation of application Ser. No.07/384,589, filed Jul. 25, 1989, now U.S. Pat. No. 4,976,898, which is aDivision of application Ser. No. 07/042,087, filed Apr. 24, 1987, nowU.S. Pat. No. 4,863,769, which is a continuation application Ser. No.06/745,236, filed Jun. 17, 1985, now abandoned.

The entire disclosures of applications: Ser. No. 07/779,676, filed Oct.21, 1991, now U.S. Pat. No. 5,256,428 Ser. No. 07/501,986filed Mar. 28,1990; now U.S. Pat. No. 5,059,481, Ser. No. 07/384,589, filed Jul. 25,1989, now U.S. Pat. No. 4,976,898 Ser. No. 07/042,087, filed Apr. 24,1987, now U.S. Pat. No. 4,863,769 and Ser. No. 06/745,236, filed Jun.17, 1985, which is now abandoned, are hereby incorporated by referencein their entireties.

FIELD OF THE INVENTION

This invention relates to puncture resistant, heat-shrinkable films, andmore particularly, to such films having high flexibility over a widetemperature range, and excellent stress crack resistance. The filmscontain very low density polyethylene copolymers.

BACKGROUND OF THE INVENTION

The packaging of food articles such as poultry, fresh red meat, andprocessed meat products requires tough, puncture resistant, yetflexible, film materials. It is also desirable that the film materialsbe suitable for use in fabricating bags for packaging such food articlesby the shrink wrapping method. Generally, the shrink wrapping method ispredicated upon the heat-shrinking property of the bag by placing agiven food article or articles into the bag, and thereafter exposing thebag to a heat source such as a flow of hot air, infrared radiation, hotwater, and the like, thereby causing the bag to shrink and come intointimate contact with the contours of the food article or articles. Thepackaged article prepared by this packaging method has an attractiveappearance which adds to the commodity value of the wrapped article, itscontents are kept in a hygienic condition, and it allows shoppers toexamine the quality of the contents of the packaged article.

For example, in commercial poultry packaging operations, monolayer filmsmade from polyethylene or ethylene-vinyl acetate copolymers, andmultilayer films containing ethylene-vinyl acetate copolymers areutilized extensively. Likewise, in the packaging of fresh red meat andprocessed meat products, multilayer heat-shrinkable films containingethylene-vinyl acetate copolymers in one or more layers of the films arecommonly employed. Ethylene-vinyl acetate copolymers have been commonlyemployed in such applications because of their toughness and lowtemperature shrinking characteristics. However, film materials in one ormore film layers which possess the shrinking characteristics ofethylene-vinyl acetate copolymers and which provide additional toughnessare generally very expensive materials, such as ionomers orpolyurethanes. Even tougher film materials are desired for variedpackaging applications, but heretofore they have not been available.

In providing such film materials, however, it must be remembered thatthe film material must be stretchable in order to provide a shrinkablefilm that will heat-shrink within a specified range of percentages,e.g., from about 30 to 50 percent at 90° C. in both the machine and thetransverse directions. Further, the film must be heat sealable in orderto be able to fabricate bags from the film, and the heat sealed seamsmust not pull apart during the heat shrinking operation. In addition,the film must resist puncturing by sharp edges, such as bone edges,during the heat-shrinking operation; and there must be adequate adhesionbetween the several layers of a multilayer film so that delaminationdoes not occur, either during the heat-shrinking operation, or duringexposure of the film to the relatively high temperatures that may bereached during shipping and storage of the film in the summertime.

Accordingly, although the known films meet many of the requirements forpackaging applications, the need still exists for improvedheat-shrinkable films and bags fabricated therefrom.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a biaxiallystretched, heat-shrinkable, thermoplastic film comprising very lowdensity polyethylene copolymer. The very low density polyethylenepolymer comprises ethylene copolymerized with higher alpha olefinscontaining from 3 to 8 carbon atoms such as propylene, butene, pentene,hexene, heptene, and octene. These ethylene copolymers have a densitybelow about 0.91 g/cm³ and a 1% secant modulus below about 140,000 kPa,and preferably have a density of from about 0.86 g/cm³ to about 0.91g/cm³ and a 1% secant modulus of from about 600 kPa to about 100,000kPa. Further, the ethylene copolymers have a standard or normal loadmelt index of up to about 25.0 g/10 minutes, and preferably of fromabout 0.2 g/10 minutes to about 4.0 g/10 minutes. In addition, theethylene copolymers have a high load melt index (HLMI) of up to about1000 g/10 minutes.

DETAILED DESCRIPTION OF THE INVENTION

More particularly, the ethylene copolymers employed in the filmmaterials of the instant invention are preferably prepared in afluidized bed polymerization process by continuously contacting, in suchfluidized bed, at a temperature of from 10° C. up to 80° C., a gaseousmixture containing (a) ethylene and at least one higher alpha olefin ina molar ratio of such higher alpha olefin to ethylene of from 0.35:1 to8.0:1, and (b) at least 25 mol percent of a diluent gas, with a catalystcomposition prepared by forming a precursor composition from a magnesiumcompound, titanium compound, and electron donor compound; diluting saidprecursor composition with an inert carrier; and activating the dilutedprecursor composition with an organoaluminum compound.

Fluid bed reactors suitable for continuously preparing ethylenecopolymers have been previously described and are well known in the art.Fluid bed reactors useful foe this purpose are described, e.g., in U.S.Pat. Nos. 4,302,565 and 4,302,566. Said patents likewise disclosecatalyst compositions suitable for preparing such copolymers.

In order to produce ethylene copolymers having a density below 0.91g/cm³ by means of a fluid bed process, it is necessary to employ gaseousreaction mixtures containing higher amounts of higher alpha olefincomonomer vis-a-vis the amount of ethylene employed, than are employedto produce copolymers having a density greater than 0.91 g/cm³. By theaddition of progressively larger amounts of such higher olefin to themixture, copolymers having progressively lower densities are obtained atany given melt index. The amount of higher olefin needed to achievecopolymers of a given density will vary from olefin to olefin, under thesame conditions, with larger amounts of such higher olefin required asthe number of carbon atoms in the olefin decreases. Generally, in orderto produce copolymers having a density of less than 0.91 g/cm³, it isnecessary to employ reaction mixtures containing such higher olefin andethylene in a molar ratio of higher olefin to ethylene of at least0.35:1. Usually, mixtures containing such higher olefin and ethylene ina molar ratio of from 0.35:1 to 8.0:1 are employed for this purpose,with molar ratios of from 0.6:1 to 7.0:1 being preferred.

The higher alpha olefins which can be polymerized with ethylene toproduce the low density, low modulus copolymers of the present inventioncan contain from 3 to 8 carbon atoms. These alpha olefins should notcontain any branching on any of their carbon atoms closer than twocarbon atoms removed from the double bound. Suitable alpha olefinsinclude propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1,heptene-1 and octene-1. The preferred alpha olefins are propylene,butene-1, hexene-1, 4-methylpentene-1 and octene-1.

If desired, one or more dienes, either conjugated or non-conjugated, maybe present in the reaction mixture. Such dienes may be employed in anamount of from 0.1 mol percent to 10 mol percent of the total gaseousmixture fed to the fluid bed, and are preferably present in an amount offrom 0.1 mol percent to 8 mol percent. Such dienes may include, forexample butadiene, 1,4-hexadiene, 1,5-hexadiene, vinyl norbornene,ethylidene norbornene and dicyclopentadiene.

In order to prevent the formation of polymer agglomerates and sustainpolymerization on a continuous basis, when employing reaction mixturescontaining the high ratios of higher alpha olefin comonomer to ethylenewhich are required to produce the desired copolymers having a densitybelow 0.91 g/cm³ it has been found necessary to dilute the reactionmixture with a large quantity of a diluent gas. Dilution of the reactionmixture with a diluent gas in this manner serves to reduce the tackinessof the polymers produced, which is the main cause of such agglomeration.Ordinarily the diluent gas should make up at least 25 mol percent of thetotal gaseous mixture fed to the fluid bed in order to prevent suchagglomeration. Preferably, the gaseous mixture contains from 33 molpercent to 95 mol percent of such gas, and most preferably from 40 molpercent to 70 mol percent. By a "diluent" gas is meant a gas which isnonreactive under the conditions employed in the polymerization reactor,i.e., does not decompose and/or react with the polymerizable monomersand the components of the catalyst composition under the polymerizationconditions employed in the reactor, other than to terminate polymerchain growth. In addition, such gas should be insoluble in the polymerproduct produced so as not to contribute to polymer tackiness. Amongsuch gases are nitrogen, argon, helium, methane, ethane, and the like.

Hydrogen may also be employed as a diluent gas. In such event, thediluent serves not only to dilute the reaction mixture and preventpolymer agglomeration, but also acts as a chain transfer agent toregulate the melt index of the copolymers produced. Generally, thereaction mixture contains hydrogen in an amount sufficient to produce ahydrogen to ethylene mol ratio of from 0.01:1 to 0.5:1. In addition tohydrogen, other chain transfer agents may be employed to regulate themelt index of the copolymers.

The gaseous reaction mixture should, of course, be substantially free ofcatalyst poisons, such as moisture, oxygen, carbon monoxide, carbondioxide, acetylene and the like.

In addition to diluting the reaction mixture with a diluent gas, it isnecessary to maintain a relatively low temperature in the reactor inorder to prevent polymer agglomeration and sustain polymerization on acontinuous basis. The temperature which can be employed varies directlywith the concentration of diluent gas present in such mixture, withhigher concentrations of diluent gas permitting the use of somewhathigher temperatures without adverse effects. Likewise, the lower theconcentration of the higher alpha olefin comonomer in the reactionmixture vis-a-vis the ethylene concentration, i.e., the higher thedensity and modulus of the copolymer being produced, the higher thetemperature which can be employed. Generally, however, in order tocontinuously produce copolymers having a density below 0.91 g/cm³ and a1% secant modulus below 140,000 kPa while at the same time preventingpolymer agglomeration, the temperature should not be permitted to riseabove 80° C. On the other hand, the temperature employed must besufficiently elevated to prevent substantial condensation of thereaction mixture, including diluent gas, to the liquid state, as suchcondensation will cause the polymer particles being produced to cohereto each other and likewise aggravate the polymer agglomeration problem.This difficulty is normally associated with the use of alpha olefinshaving 5 or more carbon atoms which have relatively high dew points.While some minor condensation is tolerable, anything beyond this willcause reactor fouling. Usually temperatures of from 10° C. to 60° C. areemployed to produce copolymers having a density of from 0.86 g/cm³ to0.90 g/cm³ and a secant modulus of from 600 kPa to 100,000 kPa. Moreelevated temperatures of from 0° C. up to 80° C. are ordinarily employedin the production of copolymers having a density of from 0.90 g/cm³ upto 0.91 g/cm³ and a 1% secant modulus of from 100,000 kPa up to 140,000kPa.

Pressures of up to about 7000 kPa can be employed in preparing thecopolymers, although pressures of from about 70 kPa to 2500 kPa arepreferred.

In order to maintain a viable fluidized bed, the superficial gasvelocity of the gaseous reaction mixture through the bed must exceed theminimum flow required for fluidization and preferably is at least 0.2feet per second above the minimum flow. Ordinarily the superficial gasvelocity does not exceed 5.0 feet per second, and most usually no morethan 2.5 feet per second is sufficient.

The catalyst compositions employed in preparing the copolymers areproduced by forming a precursor composition from a magnesium compound,titanium compound, and electron donor compound; diluting said precursorcomposition with an inert carrier; and activating the diluted precursorcomposition with an organoaluminum compound.

The precursor composition is formed by dissolving at least one titaniumcompound and at least one magnesium compound in at least one electrondonor compound at a temperature of from about 20° C. up to the boilingpoint of the electron donor compound. The titanium compound(s) can beadded to the electron donor compound(s) before or after the addition ofthe magnesium compound(s), or concurrent therewith. The dissolution ofthe titanium compound(s) and the magnesium compound(s) can befacilitated by stirring, and in some instances by refluxing these twocompounds in the electron donor compound(s). After the titaniumcompound(s) and the magnesium compound(s) are dissolved, the precursorcomposition may be isolated by crystallization or by precipitation withan aliphatic or aromatic hydrocarbon containing from 5 to 8 carbonatoms, such as hexane, isopentane or benzene. The crystallized orprecipitated precursor composition may be isolated in the form of fine,free-flowing particles having an average particle size of from about 10microns to about 100 microns after drying at temperatures up to 60° C.

About 0.5 mol to about 56 mols, and preferably about 1 mol to about 10mols, of the magnesium compound(s) are used per mol of the titaniumcompound(s) in preparing the precursor composition.

The titanium compound(s) employed in preparing the precursor compositionhas the structure

    Ti(OR).sub.a X.sub.b

wherein R is an aliphatic or aromatic hydrocarbon radical containingfrom 1 to 14 carbon atoms, or COR' where R' is an aliphatic or aromatichydrocarbon radical containing from 1 to 14 carbon atoms.

X is selected from the group consisting of Cl, Br, I, and mixturesthereof.

a is 0, 1 or 2, b is 1 to 4 inclusive, and a+b=3 or 4.

Suitable titanium compounds include TiCl₃, TiCl₄, Ti(OCH₃)Cl₃, Ti(OC₆H₅)Cl₃, Ti(OCOCH₃)Cl₃ and Ti(OCOC₆ H₅)Cl₃. TiCl₃ is preferred becausecatalysts containing this material show higher activity at the lowtemperatures and monomer concentrations employed in preparing thecopolymers.

The magnesium compound(s) employed in preparing the precursorcomposition has the structure

    MgX.sub.2

wherein X is selected from the group consisting of Cl, Br, I, andmixtures thereof.

Suitable magnesium compounds include MgCl₂, MgBr₂ and MgI₂. AnhydrousMgCl₂ is particularly preferred.

The electron donor compound(s) employed in preparing the precursorcomposition is an organic compound which is liquid at 25° C. and inwhich the titanium and magnesium compounds are soluble. The electrondonor compounds are known as such, or as Lewis bases.

Suitable electron donor compounds include the alkyl esters of aliphaticand aromatic carboxylic acids, aliphatic ethers, cyclic ethers andaliphatic ketones. Among these electron donor compounds, those preferredare alkyl esters of saturated aliphatic carboxylic acids containing from1 to 4 carbon atoms; alkyl esters of aromatic carboxylic acidscontaining from 7 to 8 carbon atoms; aliphatic ethers containing from 2to 8 carbon atoms but preferably from 4 to 5 carbon atoms; cyclic etherscontaining from 4 to 5 carbon atoms, but preferably mono- or di-etherscontaining 4 carbon atoms; and aliphatic ketones containing from 3 to 6carbon atoms, but preferably from 3 to 4 carbon atoms. The mostpreferred of these electron donor compounds include methyl formate,ethyl acetate, butyl acetate, ethyl ether, tetrahydrofuran, dioxane,acetone and methyl ethyl ketone.

After the precursor composition has been prepared, it is diluted with aninert carrier material by (1) mechanically mixing or (2) impregnatingsuch composition into the carrier material.

Mechanical mixing of the inert carrier and precursor composition iseffected by blending these materials together using conventionaltechniques. The blended mixture suitably contains from about 3 percentby weight to about 50 percent by weight of the precursor composition.

Impregnation of the inert carrier material with the precursorcomposition may be accomplished by dissolving the precursor compositionin the electron donor compounds, and then admixing the support with thedissolved precursor composition to impregnate the support. The solventis then removed by drying at temperatures up to about 85° C.

The support may also be impregnated with the precursor composition byadding the support to a solution of the chemical raw materials used toform the precursor composition in the electron donor compound, withoutisolating the precursor composition from said solution. The excesselectron donor compound is then removed by drying at temperatures up toabout 85° C.

When thus made as disclosed above, the blended or impregnated precursorcomposition has the formula

    Mg.sub.m Ti(OR).sub.n X.sub.p[ED].sub.q

wherein R is an aliphatic or aromatic hydrocarbon radical containingfrom 1 to 14 carbon atoms, or COR' wherein R' is also an aliphatic oraromatic hydrocarbon radical containing from 1 to 14 carbon atoms.

X is selected from the group consisting of Cl, Br, I, and mixturesthereof.

ED is an electron donor compound

m is 0.5 to 56, but preferably 1.5 to 5,

n is 0, 1 or 2,

p is 2 to 116, but preferably 6 to 14, and

q is 2 to 85, but preferably 3 to 10.

Suitably, the impregnated carrier material contains from about 3 percentby weight to about 50 percent by weight, but preferably from about 10percent by weight to about 30 percent by weight, of the precursorcomposition.

The carrier materials employed to dilute the precursor composition aresolid, particulate, porous materials which are inert to the othercomponents of the catalyst composition, and to the other activecomponents of the reaction system. These carrier materials includeinorganic materials such as oxides of silicon and/or aluminum. Thecarrier materials are used in the form of dry powders having an averageparticle size of from about 10 microns to about 250 microns, butpreferably from about 20 microns to about 150 microns. These materialsare also porous and have a surface area of at least 3 square meters pergram, and preferably at least 50 square meters per gram. Catalystactivity or productivity can apparently be improved by employing asilica support having average pore sizes of at least 80 Angstrom units,but preferably at least 100 Angstrom units. The carrier material shouldbe dry, that is, free of absorbed water. Drying of the carrier materialcan be effected by heating, e.g., at a temperature of at least 600° C.when silica is employed as the support. Alternatively, when silica isemployed, it may be dried at a temperature of at least 200° C. andtreated with about 1 weight percent to about 8 weight percent of one ormore of the aluminum activator compounds described below. Modificationof the support with an aluminum compound in this manner provides thecatalyst composition with increased activity and also improves polymerparticle morphology of the resulting ethylene copolymers. Otherorganometallic compounds, such as diethylzinc, may also be used tomodify the support.

To be useful in producing the ethylene copolymers, the precursorcomposition must be activated with a compound capable of transformingthe titanium atoms in the precursor composition to a state which willcause ethylene to effectively copolymerize with higher alpha olefins.Such activation is effected by means of an organoaluminum compoundhaving the structure

    AI(R").sub.d X'.sub.e H.sub.f

wherein X'is Cl or OR'".

R" and R'"are saturated hydrocarbon radicals containing from 1 to 14carbon atoms, which radicals may be the same or different.

e is 0 to 1.5,

f is 0 or 1, and

d+e+f=3.

Such activator compounds can be employed individually or in combinationthereof and include compounds such as Al(C₂ H₅)₃, Al(C₂ H₅)₂ Cl, Al₂ (C₂H₅)₃ Cl₃, Al(C₂ H₅)₂ H, Al(C₂ H₅)₂ (OC₂ H₅), Al(i-C₄ H₉)₃, Al(i-C₄ H₉)₂H, Al(C₆ H₁₃)₃ and Al(C₈ H₁₇)₃.

If desired, the precursor composition may be partially activated beforeit is introduced into the polymerization reactor. However, anyactivation undertaken outside of the polymerization reactor should belimited to the addition of an amount of activator compound which doesnot raise the molar ratio of activator compound electron donor in theprecursor composition beyond 1.4:1. Preferably, when activation iseffective outside the reactor in this manner, the activator compound isemployed in an amount which will provide the precursor composition withan activator compound:electron donor molar ratio of from about 0.1:1 toabout 1.0:1. Such partial activation is carried out in a hydrocarbonsolvent slurry followed by drying of the resulting mixture to remove thesolvent at temperatures of from about 20° C. to about 80° C., andpreferably from about 50° C. to about 70° C. The resulting product is afree-flowing solid particulate material which can be readily fed to thepolymerization reactor where the activation is completed with additionalactivator compound which can be the same or a different compound.

Alternatively, when an impregnated precursor composition is employed, itmay, if desired, be completely activated in the polymerization reactorwithout any prior activation outside of the reactor, in the mannerdescribed in European patent publication No. 12,148.

The partially activated or totally unactivated precursor composition andthe required amount of activator compound necessary to completeactivation of the precursor composition are preferably fed to thereactor through separate feed lines. The activator compound may besprayed into the reactor in the form of a solution thereof in ahydrocarbon solvent such as isopentane, hexane or mineral oil. Thissolution usually contains from about 2 weight percent to about 30 weightpercent of the activator compound. The activator compound is added tothe reactor in such amounts as to provide, in the reactor, a totalaluminum:titanium molar ratio of from about 10:1 to about 400:1, andpreferably from about 25:1 to about 60:1.

In the continuous gas phase fluid bed process, discrete portions of thepartially activated or totally unactivated precursor composition arecontinuously fed to the reactors, together with discrete portions of theactivator compound needed to complete the activation of the partiallyactivated or totally unactivated precursor composition during thecontinuing polymerization reaction in order to replace active catalystsites that are expended during the course of the reaction.

By operating under the polymerization conditions described herein, andmore fully disclosed by F. J. Karol et al in U.S. Ser. No. 587,005 filedon Mar. 13, 1984 titled "Preparation of low density, low modulusethylene copolymers in a fluidized bed", it is possible to continuouslypolymerize ethylene in a fluidized bed with one or more higher alphaolefins containing from 3 to 8 carbon atoms, and optionally also withone or more dienes, to produce ethylene copolymers having a densitybelow 0.91 g/cm³ and a 1% secant modulus below 140,000 kPa. By"continuously polymerize", as used herein, is meant the capability ofuninterrupted polymerization for weeks at a time i.e., at least inexcess of 168 hours and usually in excess of 1000 hours, without reactorfouling due to the production of large agglomerations of polymer.

The copolymers produced in accordance with the aforedescribed processusually have a density of from 0.86 g/cm³ to 0.90 g/cm³ and a 1% secantmodulus of from 600 kPa to 100,000 kPa. Such copolymers contain no morethan 94 mol percent of polymerized ethylene and at least 6 mol percentof polymerized alpha olefin containing from 3 to 8 carbon atoms and,optionally, polymerized diene. When polymerized diene is present, thepolymer contains from 0.01 mol percent to 10 mol percent of at least onesuch diene, from 6 mol percent to 55 mol percent of at least onepolymerized alpha olefin containing from 3 to 8 carbon atoms, and from35 mol percent to 94 mol percent of polymerized ethylene.

The molar ratios of propylene to ethylene which must be employed in thereaction mixture to produce copolymers having a given propylene contentare illustrated in Table 1 below. When alpha olefins higher thanpropylene are employed, like results can be obtained with lower ratiosof such higher alpha olefin to ethylene in the reaction mixture.

                  TABLE 1                                                         ______________________________________                                        C.sub.3 H.sub.6 /C.sub.2 H.sub.4 Ratio                                                       Mol % C.sub.3 H.sub.6                                                                     Mol % C.sub.2 H.sub.4                              In Reaction Mixture                                                                          In Copolymer                                                                              In Copolymer                                       ______________________________________                                        0.7             6          94                                                 1.5            12          88                                                 3.0            25          75                                                 6.0            50          50                                                 8.0            62          38                                                 ______________________________________                                    

The ethylene copolymers produced in accordance with the aforedescribedprocess have a standard or normal load melt index of from greater than 0g/10 minutes to about 25.0 g/10 minutes, and preferably of from about0.2 g/10 minutes to about 4.0 g/10 minutes. Such polymers have a highload melt index (HLMI) of from greater than 0 g/10 minutes to about 1000g/10 minutes. The melt index of a polymer varies inversely with itsmolecular weight and is a function of the polymerization temperature ofthe reaction, the density of the polymer, and the hydrogen/monomer ratioin the reaction system. Thus, the melt index is raised by increasing thepolymerization temperature, by increasing the ratio of higher alphaolefin to ethylene in the reaction system, and/or by increasing thehydrogen/monomer ratio.

The ethylene copolymers produced in accordance with the aforedescribedprocess have a melt flow ratio (MFR) of from about 22 to about 40,molecular weight distribution (M_(w) /M_(n)) of a and preferably of fromabout 26 to about 35. Melt flow ratio is another means of indicating thepolymer. A MFR in the range of from about 22 to about 40 corresponds toa M_(w/M) _(n) of from about 2.7 to about 6.5, and a MFR in the range offrom about 26 to about 35 corresponds to a M_(w) /M_(n) of from about2.9 to about 4.8.

The ethylene copolymers produced, typically, have a residual catalystcontent, in terms of parts per million of titanium metal, of less than10 parts per million (ppm) at a productivity level of at least 100,000pounds of polymer per pound of titanium. The copolymers are readilyproduced with such catalyst compositions at productivities of up toabout 500,000 pounds of polymer per pound of titanium.

The ethylene copolymers are granular materials having an averageparticle size on the order of from about 0.01 to about 0.07 inches, andusually of from about 0.02 to about 0.05 inches in diameter. Theparticle size is important for the purpose of readily fluidizing thepolymer particles in the fluid bed reactor. These granular materialsalso contain no more than 4.0 percent of fine particles having adiameter of less than 0,005 inches. The ethylene copolymers typicallyhave a bulk density of from about 16 pounds per cubic foot to about 31pounds per cubic foot.

The properties of the ethylene copolymers are determined by thefollowing test methods:

Density

ASTM D-1505. A plaque is made and conditioned for one hour at 100° C. toapproach equilibrium crystallinity. Measurement for density is then madein a density gradient column and density values are reported asgrams/cm³.

Melt Index (MI)

ASTM D-1238, Condition E. Measured at 190° C. and reported as grams per10 minutes.

Flow Index (HLMI)

ASTM D-1238, Condition F. Measured at 10 times the weight used in themelt index test above.

Melt Flow Ratio (MFR)

Ratio of Flow Index: Melt Index

Bulk Density

ASTM D-1895, Method B. The resin is poured via a 3/8 "diameter funnelinto a 400 ml graduated cylinder to the 400 ml line without shaking thecylinder, and weighed by difference.

Average Particle Size

Calculated from sieve analysis data measured according to ASTM D-1921,Method A, using a 500 g sample. Calculations are based on weightfractions retained on the screens.

Molecular Weight Distribution, M_(w) /M_(n)

Gel Permeation Chromatography. Styrogel column packing: (Pore sizepacking sequence is 10⁷, 10⁵, 10⁴, 10³, 60A° ). Solvent isperchloroethylene at 117° C. Detection: infrared at 3.45μ.

1% Secant Modulus

ASTM D-638. Film strips 10"×0.5" are clamped at a 5 inch gauge lengthand deformed at a Jaw separation rate of 0.2 in./min. A force elongationtrace is determined. Secant modulus is the slope of a line drawn fromthe origin to the load at 1% deformation. Deformation to determined bycrosshead position. Normalizing by the specimen's undeformedcross-sectional area, secant modulus is reported in kPa.

In general, it has been found that when the very low density ethylenecopolymers are formed into films, and the films are biaxially stretched,the stretched films provide exceptionally high shrinkage values atelevated temperatures, for example, such as at about 90° C., compared tofilms made from ethylene-vinyl acetate copolymers. The biaxiallystretched, very low density ethylene copolymer films of this inventionheat-shrink from about 30 percent to about 50 percent at a temperatureof about 90° C. in both the machine direction and transverse direction.Further, stretched films made from very low density ethylene copolymershave excellent tensile, elongation, and puncture toughness properties.Due to these properties, the films are improved materials forfabricating into bags for packaging food articles such as poultry,primal meat cuts, and processed meat products.

Illustrative, non-limiting examples of the features and practice of theinvention are set out below. The parts and percentages set forth hereinrefer to parts by weight and percentages by weight, respectively, unlessspecifically stated otherwise.

In the examples, the following test methods were used to determine theproperties of the resins and the films described in Example 1. Tensilestrength and elongation at break values were obtained pursuant to ASTMMethod D-882, procedure A. Density values were obtained by ASTM MethodD-1505. Dynamic puncture values were obtained by employing a DynamicBall Burst Tester, Model 13-8, manufactured by Testing Machines, Inc.,Amityville, Long Island, N. Y. A special tip designed to simulate asharp-boned surface was employed to replace the spherical-shaped impacthead of the apparatus. This modified testing device measured energy inunits of kilogram-centimeters.

Shrinkage values were obtained by measuring unrestrained shrink at 90°C. for five seconds. In more detail, a 1 or 2 liter beaker is filledwith water which is heated to about 100° C. Four machine direction (MD)shrinkage test samples are cut to 12 cm. machine direction by 1.27 cm.transverse direction (TD). Four transverse direction shrinkage testsamples are cut to 12 cm. transverse direction by 1.27 cm. machinedirection. Both sets of samples are marked with a short cut exactly 10cm. from one end for identification. The water bath temperature isbrought to 90° C., and each sample is completely immersed in the waterbath for five seconds and removed therefrom. After shrinking, thedistance between the end of the sample and the 10 cm. mark is measuredto the closest 0.1 cm. The difference between the final length and theoriginal 10 cm. is multiplied by 10 to obtain the percent change. If thesample shrinks, the value is negative, and if the sample stretches, thevalue is positive. The average of the four samples is calculated forboth of the machine direction and transverse direction samples.

EXAMPLE I

This example illustrates the comparative heat-shrinking properties of avery low density polyethylene (VLDPE) film made by (1) the free orsimple bubble extrusion process, and by (2) the "double bubble" methoddescribed in Pahlke U.S. Pat. No. 3,555,604. The "double bubble"manufacturing method results in a film which has been biaxiallystretched. More particularly, in the practice of the "double bubble"method, the primary tube (extruded film) is stretched in the machinedirection, cooled, reheated, and then stretched in the machine andtransverse direction. By comparison, in the free or simple bubbleextrusion process, the tube is blown and simultaneously stretched in themachine and transverse directions, and then cooled.

The very low density polyethylene material employed to make the filmshad a density of about 0.906 g./cm³, and a melt index of about 0.88decigram per minute, and is available from Union Carbide Corporation,Danbury, Conn. under the designation UCAR® FLX DFDA-1137. The films madeby the simple bubble extrusion process and by the "double bubble" methodwere evaluated for percent shrinkage at 85° C., 90° C., and 95° C. inaccordance with the aforedescribed test method. The results of theseevaluations are summarized below in Table 2.

                  TABLE 2                                                         ______________________________________                                        Percent Heat Shrinkage of Simple Bubble and                                   Double Bubble Production                                                      Very Low Density Polyethylene                                                                Simple     Double                                              Shrinkage      Bubble     Bubble                                              Temperature (°C.)                                                                     MD/TD (%)  MD/TD (%)                                           ______________________________________                                        85             2/3        42/45                                               90             3/3        52/53                                               95             3/3        58/58                                               ______________________________________                                    

It can be seen from the data in Table 2 that the film made from the verylow density polyethylene material by the simple bubble extrusion processhas very low heat shrinkage properties, whereas the film made by the"double bubble" method has exceptionally high shrinkage values for boththe machine direction (MD) and the transverse direction (TD) samples.

EXAMPLE II

This example illustrates the comparative properties of a biaxiallystretched very low density polyethylene (VLDPE) film, film A, with thoseof biaxially stretched films made from low density polyethylene (LDPE),film B; linear, low density polyethylene (LLDPE), film C; ethylene-vinylacetate copolymer having a vinyl acetate content of 12 weight percent(EVA-12), film D; ethylene-vinyl acetate copolymer having a vinylacetate content of 3 weight percent (EVA-3), film E; and anethylene-methacrylic acid ionic copolymer (ionomer) having a melt flowindex of about 1.3 g./10 min. and a specific gravity of about 0.94g./cm³, commercially available as Surlyn 1601 from E. I. dupont deNemours and Co., Wilmington, Del., film F. Film A was made from a verylow density ethylene copolymer having a density of about 0.90 g./cm³,and a melt index of about 0.84 decigram per minute. The biaxiallystretched monolayer films were made pursuant to the "double bubble"method described in Pahlke U.S. Pat. No. 3,555,604. The biaxiallystretched films were evaluated for heat shrink properties, punctureresistance, tensile strength, and elongation. The results of theseevaluations are summarized below in Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Physical Properties of Biaxially Stretched Monolayer Films                                             Shrink %                                                                            Tensile                                           Resin       Melt                                                                              Melting                                                                             (at 90° C.)                                                                  Strength                                                                           Elongation                                                                          Puncture                            Film                                                                             Type   Density                                                                            Index                                                                             Point (°C.)                                                                  MD/TD (psi)                                                                              (%)   (kg-cm/mil)                         __________________________________________________________________________    A  VLDPE  0.90 0.84                                                                              116   51/54 7650 400   2.4                                 B  LDPE   0.917                                                                              0.1 104   18/28 6700 225   0.9                                 C  LLDPE  0.918                                                                              0.65                                                                              118   18/25 7100 325   1.1                                 D  EVA-12 0.940                                                                              0.25                                                                               98   37/46 7400 275   2.5                                 E  EVA-3  0.921                                                                              0.25                                                                              104   23/35 8200 210   1.1                                 F  IONOMER                                                                              0.950                                                                              1.3  92   57/65 8600 110   1.3                                 __________________________________________________________________________

It can be seen from the data in Table 3 that a biaxially stretchedmonolayer film made from VLDPE has exceptionally high shrinkage valuesat 90° C. in spite of a relatively high melting point as compared to EVAresins, and also substantially higher shrinkage values at 90° C.compared with LDPE and LLDPE. The data for films B, C, D, E and F showthat the shrinkage values of the films generally decrease as the meltingpoint of the resins increase, whereas although the melting point of theVLDPE resin (film A) is high, the film has high shrinkage values. Inaddition, a biaxially stretched monolayer film made from VLDPE hasexcellent tensile and elongation properties, and exceptional puncturetoughness properties. That is, from the data in Table 3, it can be seenthat a biaxially stretched monolayer film made from VLDPE has betterelongation properties than LDPE, LLDPE, EVA-12, EVA-3, and the instantionomer material. For example, the data shows that the VLDPE film may bestretched 400% or about four times its original length before it breaks.Thus, a biaxially stretched monolayer film made from VLDPE has thephysical properties which are highly desirable for use as aheat-shrinkable bag for packaging frozen poultry, as well as otherproducts.

EXAMPLE III

In this example, bags for packaging poultry were evaluated for shrinktunnel performance. All bags were made from films obtained pursuant tothe method described in Pahlke U.S. Pat. No. 3,555,604. The bagsdesignated sample A were made from a biaxially stretched monolayer filmhaving a thickness of about 2.25 mils prepared from a VLDPE resin havinga melt index of about 0.14 decigram per minute, and a density of about0.90 g./cm³ The bags designated sample B were conventional poultry bagsemployed as controls. The control bags were prepared from a biaxiallystretched monolayer film having a thickness of about 2.25 mils made witha blend containing 85 percent by weight of an ethylene-vinyl acetatecopolymer having a vinyl acetate content of 3 weight percent, and a meltindex of 0.25 decigram per minute, and 15 percent by weight of a highdensity polyethylene having a melt index of about 0.15 decigram perminute and a density of about 0.953 gram per cubic centimeter.

The results of the visual screening evaluations are summarized below inTable 4.

                  TABLE 4                                                         ______________________________________                                        Monolayer Film Packaging Test (Shrink Tunnel Performance)                     Film/Package Appearance After Shrink                                          Shrink Tunnel                                                                           Package Appearance                                                  Temperature                                                                             Property       Sample A  Sample B                                   ______________________________________                                        165° F.                                                                          Shrinkage      6         4                                                    Gloss          7         9                                                    Haze           5         9                                          175° F.                                                                          Shrinkage      7         5                                                    Gloss          7         9                                                    Haze           5         9                                          185° F.                                                                          Shrinkage      9         5                                                    Gloss          7         9                                                    Haze           5         9                                          195° F.                                                                          Shrinkage      9         6                                                    Gloss          7         9                                                    Haze           5         9                                          205° F.                                                                          Shrinkage      7         7                                                    Gloss          7         9                                                    Haze           5         9                                          ______________________________________                                         1 = Poor                                                                      9 = Excellent: High Shrink, High Gloss, Low Haze                              Values of at least 4 are considered acceptable.                          

The test results show that the sample A bags had substantially improvedshrinkage properties compared to the sample B bags at shrink tunneltemperatures between 165° F. and 195° F., and similar properties at 205°F. However, their gloss and haze values are somewhat lower than those ofthe sample B bags, but these values are still acceptable.

EXAMPLE IV

In this example, heat-shrinkable biaxially stretched multilayer filmswere prepared for evaluation as bags for packaging primal meat cuts. Thefilms were evaluated for shrink, tensile strength, elongation, andpuncture resistance properties. The following resin materials wereemployed to make the films.

Ethylene-Vinyl Acetate (EVA) Copolymer

12 weight percent vinyl acetate, 0.25 melt index.

Polyvinylidene Chloride (PVDC) Copolymer

84 to 87 weight percent vinylidene chloride, 13 to 16 weight percentvinyl chloride.

Very Low Density Polyethylene (VLDPE) Copolymer

Ethylene copolymer having a density of 0.906 g/cm³, and a melt index of0 92 decigram per minute.

Table 5 summarizes the resin compositions employed to make the indicatedbiaxially stretched multilayer films.

                  TABLE 5                                                         ______________________________________                                        Multilayer Film Compositions                                                           First                 Second                                                  Outer Layer   Core    Outer Layer                                    Film     (Bag Inner Layer)                                                                           Layer   (Bag Outer Layer)                              ______________________________________                                        A (Control)                                                                            EVA           PVDC    EVA                                            B        EVA           PVDC    90% EVA                                                                       10% VLDPE                                      C        EVA           PVDC    75% EVA                                                                       25% VLDPE                                      ______________________________________                                    

The biaxially stretched multilayer films were produced pursuant to theprocess disclosed in U.S. Pat. No. 3,555,604 by coextrusion through amultilayer die and subsequent biaxial stretching of the primary tube.The resultant biaxially stretched films had an average total thicknessof about 2.5 mils, wherein the first outer layer had an averagethickness of about 1.5 mils, the core layer had an average thickness ofabout 0.35 mil, and the second outer layer had an average thickness ofabout 0.65 mil. The results of the aforementioned evaluations are shownbelow in Table 6.

                  TABLE 6                                                         ______________________________________                                        Physical Properties of Biaxially Stretched                                    Multilayer Films                                                                              Tensile                                                             Shrink %  Strength  Elongation                                                at 90° C.                                                                        (psi)     (%)      Puncture                                   Film  MD/TD     MD/TD     MD/TD    (cm-kg/mil)                                ______________________________________                                        A     38/51     6400/9000 195/175  1.4                                        B     34/53     6900/9200 210/180  1.5                                        C     41/52     7500/9500 240/195  1.8                                        ______________________________________                                    

It can be seen from the data in Table 6 that a biaxially stretchedmultilayer film comprising ethylene-vinyl acetate outer layer blendscontaining VLDPE have improved tensile strengths, ultimate elongationand puncture strength compared with an outer layer containing 100%ethylene-vinyl acetate copolymer. Thus, a biaxially stretched multilayerfilm made with blends of VLDPE in the outer layer has the propertieswhich are highly desirable for use as a heat-shrinkable bag forpackaging fresh red meat and processed meat products.

Therefore, the novel film compositions of this invention have been shownto possess the physical properties required for use in packaging foodarticles such as frozen poultry, primal meat cuts and processed meatproducts. Furthermore, the film compositions of the present inventionalso have the toughness required during the biaxial stretching process,in order to provide a substantially stable operation with few bubblebreaks, while providing a film possessing the requisite physicalproperties with respect to shrinkage characteristics.

Accordingly, the film compositions of this invention comprise abiaxially stretched very low density polyethylene copolymer. A preferredbiaxially stretched monolayer film composition comprises a very lowdensity polyethylene copolymer having a density of between about 0.86g./cm.³ and about 0.91 g./cm.³, and a melt index of up to about 25.0g./10 minutes because such provides a film with improved shrinkingproperties. Such monolayer films are particularly suitable for use infabricating heat-shrinkable bags for packaging poultry products.

In a further embodiment of the film compositions of this invention, thefilm composition comprises a biaxially stretched multilayer filmcontaining a very low density polyethylene copolymer having a density ofbetween about 0.86 g./cm.³ and about 0.91 g./cm.³, and a melt index ofup to about 25.0 g./10 minutes because these films have improved tensilestrengths, ultimate elongation and puncture strength properties, and areheat-shrinkable. Such multilayer films are especially suitable for usein fabricating heat-shrinkable bags for packaging primal meat cuts andprocessed meats. For example, the multilayer film composition maycomprise a first outer layer of an ethylene-vinyl acetate copolymer; acore layer of a barrier film such as a polyvinylidene chloride copolymeror an ethylene-vinyl alcohol copolymer; and a second outer layercomprising a blend of an ethylene-vinyl acetate copolymer and frombetween about 5 weight percent and 25 weight percent, but preferablybetween about 10 weight percent and about 25 weight percent, of a verylow density polyethylene polymer as described above.

In accordance with a preferred embodiment of this invention, the firstouter layer of the multilayer film is an ethylene-vinyl acetatecopolymer containing from about 9 to about 15 weight percent of vinylacetate, based on the weight of the copolymer, said copolymer having amelt index of between about 0.1 and about 1.0 decigram per minute andbeing selected from the group consisting of (a) a single ethylene-vinylacetate copolymer and (b) a blend of ethylene-vinyl acetate copolymers.

The second outer layer of the multilayer film of this inventioncomprises an ethylene-vinyl acetate copolymer selected from the groupconsisting of (a) an ethylene-vinyl acetate copolymer having a meltindex of from about 0.1 to about 1.0 decigram per minute and a vinylacetate content of from about 3 to about 18 weight percent, andpreferably from about 10 to about 15 weight percent, based on the weightof said second ethylene-vinyl acetate copolymer, and (b) a blend of atleast two ethylene-vinyl acetate copolymers, wherein one of saidethylene-vinyl acetate copolymers has a melt index of from about 0.1 toabout 1.0 decigram per minute and a vinyl acetate content of from about10 to about 18 weight percent, based on the weight of said copolymer,and the other ethylene-vinyl acetate copolymer has a melt index of fromabout 0.1 to about 1.0 decigram per minute and a vinyl acetate contentof from about 2 to about 10 weight percent, based on the weight of saidcopolymer. The blend (b) of said at least two ethylene-vinyl acetatecopolymers has a vinyl acetate content of from about 3 to about 18weight percent, and preferably from about 10 to about 15 weight percent,based on the weight of said copolymers.

The heat-shrinkable films of this invention can be produced by knowntechniques. For example, the multilayer films may be prepared byco-extruding multiple layers into a primary tube, followed by thebiaxial stretching of the tube by known techniques. The "double-bubble"technique disclosed in Pahlke U.S. Pat. No. 3,456,04, is particularlyuseful in preparing these films. In addition, after biaxial stretching,the films of this invention may be irradiated to a dosage level ofbetween about 1 megarad and about 5 megarads, such as by passing thefilms through an electron beam irradiation unit.

The biaxially stretched, heat-shrinkable, thermoplastic monolayer film,when employed to fabricate bags for packaging frozen poultry, willgenerally have a thickness of from about 1.5 mils to about 2.75 mils. Afilm having a thickness of less than about 1.5 mils tends to bephysically weak for use in the poultry packaging industry, while a filmhaving a thickness greater than about 2.75 mils tends to cause clippingproblems and loss of vacuum in the end use application. A film thicknessrange of between about 2.0 mils and about 2.4 mils is a preferredbalance of these opposing considerations.

The biaxially stretched, heat-shrinkable, thermoplastic multilayer filmwill generally have a total thickness of from about 1.75 mils to about3.0 mils. For example, when the multilayer film is a three-layer film,the first outer layer will normally have a thickness of from about 1.1mils to about 1.6 mils, the core layer will normally have a thickness offrom about 0.25 mil to about 0.45 mil; and the second outer layer willnormally have a thickness of from about 0.4 mil to about 1.0 mil. Thethickness of the first outer layer, which is the inner layer of the bag,should be within the aforementioned range because the sealing andprocessability properties of the film layer would otherwise bediminished. The thickness of the core layer should be within theabove-indicated range because the film would provide inadequate barrierproperties if the core layer thickness is less than about 0.25 mil. Theupper limit of 0.45 mil for the core layer is primarily due to economicconsiderations. The thickness of the second outer layer, which is theouter layer of the bag, is selected in order to provide a totalthickness of the multilayer film in the range of from about 1.75 mils toabout 3.0 mils. When the total film thickness of the multilayer filmexceeds about 3.0 mils, clipping problems are encountered in that it isdifficult to gather together the open end of a bag made therefrom. Whenthe thickness of the multilayer film is less than about 1.75 mils, thebag will generally have diminished puncture resistance.

When the core layer of the multilayer film of this invention comprises apolyvinylidene chloride copolymer, it must contain at least 65 weightpercent of vinylidene chloride and a maximum of 5 weight percent ofplasticizer, based upon the weight of the polyvinylidene chloridecopolymer. The remainder of the polyvinylidene chloride copolymer ispreferably vinyl chloride, but it may also include acrylonitrile, anacrylate ester such as methyl methacrylate, or the like. Morepreferably, the polyvinylidene chloride copolymer will contain at leastabout 70 weight percent, and not more than about 95 weight percent, ofpolymerized vinylidene chloride because when the polyvinylidene chloridecopolymer contains less than about 70 weight percent vinylidene chloridethe oxygen barrier property of the copolymer is diminished. If thevinylidene chloride content is more than 95 weight percent, thepolyvinylidene chloride copolymer is generally not extrudable. Thepolyvinylidene chloride copolymer preferably contains less than 5 weightpercent plasticizer, and more preferably less than 4 weight percentplasticizer, the percentages being based on the weight of, the totalblend, including the copolymer and all additives such as theplasticizer, in order to maximize the barrier properties Of the thinfilm. Conventional plasticizers such as dibutyl sebacate and epoxidizedsoybean oil can be used.

After biaxial stretching by any suitable method well known in the art,in order to provide improved heat sealing characteristics thereto, thefilms of this invention are preferably irradiated to a dosage level ofbetween about 1 megarad and about 5 megarads, and preferably betweenabout 2 megarads and about 3 megarads, by a suitable method such as byemploying an electron beam. Irradiation at a dosage level within thisrange is necessary in order to achieve improved heat sealingcharacteristics without film discoloration. That is, when the energylevel is below the indicated range, the cross-linking obtained is notsufficient to improve the heat sealing characteristics of the films orto have any enhanced effect upon the toughness properties of the films.When the energy level is above the afore-mentioned range, filmdiscoloration occurs due to degradation of some layers, particularlywhen a core layer of polyvinylidene chloride copolymer is present.Additionally, when the energy level of Irradiation exceeds about 5megarads, the degree of film shrinkage is significantly reduced, andfurther improvements in the heat sealing characteristics and toughnessproperties of the film are not achieved.

In another aspect of this invention, bags suitable for theshrink-packaging of food articles such as poultry, primal meat cuts, andprocessed meats are provided from the afore-described films. The bagsare produced from the monolayer and multilayer films of this inventionby heat sealing. For instance, if the films of this invention areproduced in the form of tubular film, bags can be produced therefrom byheat sealing one end of a length of the tubular film or by sealing bothends of the tube end, then slitting one edge to form the bag mouth. Ifthe films of this invention are made in the form of flat sheets, bagscan be formed therefrom by heat sealing three edges of two superimposedsheets of film. When carrying out the heat sealing operation, thesurfaces which are heat sealed to each other to form seams are theaforedescribed first outer layers of the multilayer films of theinvention. Thus, for example, when forming a bag by heat sealing oneedge of a length of tubular film, the inner surface of the tube, i.e.,the surface which will be heat sealed to itself, will be the first outerlayer of the film.

In general, various conventional additives such as slip agents,anti-blocking agents, and pigments can be incorporated in the films inaccordance with conventional practice.

Although preferred embodiments of this invention have been described indetail, it is contemplated that modifications thereof may be made andsome preferred features may be employed without others, all within thespirit and scope of the broad invention.

What is claimed is:
 1. A bag comprising:a shrunken thermoplasticflexible film wherein said shrunken film comprises a biaxially stretchedvery low density polyethylene (VLDPE) which is a linear copolymer ofethylene and at least one alpha-olefin selected from the group ofbutene-1, pentene-1, hexene-1, 4-methyl pentene-1, heptene-1 andoctene-1, copolymer having a density of from about 0.86 g/cm³ to about0.91 g/cm³ and a 1% secant modulus below about 140,000 kPa, saidbiaxially stretched film having a shrinkage value of from about 30percent to about 50 percent at a temperature of 90° C. in at least oneof the machine and transverse directions prior to shrinkage of saidfilm.
 2. A bag, as defined in claim 1, wherein said bag is heat sealed.3. A bag, as defined in claim 1, wherein said bag is fabricated from afilm which is biaxially stretched as a tube.
 4. A bag, as defined inclaim 1, wherein said film which comprises very low density polyethyleneis heat sealed to itself.
 5. A bag, as defined in claim 1, wherein saidalpha-olefin comprises butene-1.
 6. A bag, as defined in claim 1,wherein said alpha-olefin comprises hexene-1.
 7. A bag, as defined inclaim 1, wherein said alpha-olefin comprises octene-1.
 8. A bag, asdefined in claim 1, wherein said density is from about 0.86 g/cm³ toabout 0.90.
 9. A bag, as defined in claim 1, wherein said density isfrom about 0.90 g/cm³ to about 0.91 g/cm³.
 10. A bag, as defined inclaim 1, wherein said copolymer has a 1% secant modulus from about 600kPa to about 100,000 kPa.
 11. A bag, as defined in claim 1, wherein saidcopolymer has a 1% secant modulus from about 100,000 kPa to about140,000 kPa.
 12. A bag, as defined in claim 1, wherein said shrinkagevalue is in both the machine and transverse direction.
 13. A bag, asdefined in claim 1, wherein said VLDPE has a melt index (M. I.) asmeasured by ASTM D-1238 condition E of greater than 0 g/10 minutes toabout 25.0 g/10 minutes.
 14. A bag, as defined in claim 13, wherein saidmelt index is from about 0.2 g/10 minutes to about 4.0 g/10 minutes. 15.A bag, as defined in claim 13, wherein said melt index is from about0.14 g/10 minutes to about 0.92 g/10 minutes.
 16. A bag, as defined inclaim 1, wherein said film consists essentially of said VLDPE copolymer.17. A bag, as defined in claim 1, wherein said film is cross-linked. 18.A packaged article, as defined in claim 1, wherein said film is amonolayer film.
 19. A bag, as defined in claim 1, wherein said film wasbiaxially stretched below the melting point of the VLDPE.
 20. A bag, asdefined in claim 1, wherein said film comprises a multilayer film.